Abstract: In the context of global climate change, carbon emissions have become an increasingly pressing concern.As one of the world’s largest carbon emitters, it is a critical strategic objective for China to achieve both carbon peaking and carbon neutrality.The Yangtze River Delta region (YRDR), as a significant growth pole of China′s economy, plays a pivotal role in enhancing carbon emission efficiency and overall carbon performance to meet national reduction targets.Utilizing data from the urban agglomeration of the YRDR from 2004 to 2022, this study analyzed the effects of regional integration on carbon performance.The fixed-effect models and spatial Durbin models were used.The empirical findings were summarized as follows: Firstly, regional integration fostered improvements in urban carbon performance.However, there existed a lag effect alongside a "snowball" effect in the development of such performance.This enhancement primarily occurred through three mechanisms: high-quality economic development, increased openness to external markets, and promotion of investment.Secondly, environmental regulation amplified the positive impact that regional integration imposed on urban carbon performance.Conversely, energy intensity exerted a negative moderating influence.Thirdly, while regional integration positively influenced carbon performance within the YRDR itself, it exhibited a negative spatial spillover effect on the neighboring areas, presenting a demonstration of a "siphon" effect.It was imperative to expedite the establishment of a unified regional carbon market along with an efficient division-of-labor system within green industrial chains.Strategies were suggested to facilitate the achievement of the "dual carbon" goals, which included the acceleration of the development of a regionally unified carbon market and a green industrial chain allocation system, the establishment of consortia for green technology research, and the optimization of the structure of foreign capital utilization.